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Dark matter was less influential in the early universe

The discovery doesn't show the early universe featured less dark matter, only that dark matter had less influence on the dynamics of early galaxies.

By Brooks Hays
Dark matter was less influential in the early universe
A diagram shows the rotational differences between a galaxy from the early or distant universe, at right, and one from the local universe, at left. Photo by European Southern Observatory

March 15 (UPI) -- Dark matter played a subordinate role in the formation and evolution of the universe's earliest generation of galaxies, new research showed. Baryonic or "normal" matter headlined.

Astronomers in Germany used ESO's Very Large Telescope to measure the rotational speeds of six large, star-rich galaxies in the distant universe. The rotations of the galaxies' outer regions measured slower than the outer parts of closer, younger spiral galaxies.

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The discrepancy, detailed in the journal Nature, suggests early galaxies featured less dark matter in their outer layers.

Baryonic matter is visible. It makes up the stars, gas and dust imaged by telescopes. Dark matter doesn't absorb or emit light. Its presence must be inferred by its gravitational effects, like its influence on galactic rotation.

"Surprisingly, the rotation velocities are not constant, but decrease further out in the galaxies," Reinhard Genzel, a researcher at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said in a news release.

Astronomers believe there are two reasons why distant galaxies differ in this way.

"Firstly, most of these early massive galaxies are strongly dominated by normal matter, with dark matter playing a much smaller role than in the local universe," Genzel said. "Secondly, these early discs were much more turbulent than the spiral galaxies we see in our cosmic neighborhood."

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Researchers found the discrepancy becomes more pronounced as they measure the rotations of even more distant galaxies.

The discovery doesn't show the early universe featured less dark matter, only that dark matter had less influence on the dynamics of early galaxies.

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